The conventional flexible display device is based on an organic material substrate. Because water isolation, oxygen barrier, and heat resistance abilities of the organic material substrate are poor, and when manufacturing a Low temperature poly-silicon (LTPS) flexible display device, a high-temperature process such as the Eximer laser annealing (ELA) is required. Accordingly, a thicker layer of nitride material or oxide material on the substrate is required as a buffering layer in order to avoid the organic material substrate from damaging. The buffering layer made of the nitride material or oxide material is generally deposited through a Plasma Enhanced Chemical Vapor Deposition (PECVD) method. The buffering layer deposited through a low-temperature deposition is loose in structure and has poor effects in water isolation and oxygen barrier. When depositing through a higher temperature, in the deposition process, the plasma bombards the organic material substrate directly such that an organic dust will pollute the device cavity and the pipeline.